NO158951B - POLYAMPHOLYTE POLYMERS AND THEIR APPLICATION FOR AA PREVENTION CORROSION AND STONE PROVISIONS IN Aqueous Systems. - Google Patents

Description

This invention relates to polyampholyte polymers and their use to prevent corrosion and deposits in aqueous systems.

Polyampholyte polymers are polymers that contain both cationic and anionic monomer units. Non-ionic monomer units may also optionally be present.

Polyampholyte polymers have found use in particular as retention aids in the paper industry, see e.g. US Patent Nos. 3,639,208 and 4,171,417. Their use as agents to prevent corrosion and deposits in aqueous systems cannot be seen to be known. Polyampholyte polymers have found some use in the oil drilling industry, see e.g. British Patent Application No. 2,044,341 A (published) and US Patent Nos. 4,293,427 and 4,330,450.

Rock deposits are crusty coatings that can be formed from a wide variety of simple and complex inorganic salts that, for a variety of reasons, accumulate on metallic surfaces of water-bearing systems. A wide variety of industrial and commercial water-carrying systems are subject to such scale problems. Stone deposits are particularly a problem in heat exchange systems where water is used, e.g. in boiler systems and open water cooling systems with recirculation of the water.

Corrosion of metal in water-bearing systems is usually caused by the presence of dissolved oxygen in the water. Corrosion inhibitors currently available include e.g. phosphorus-containing inorganic and organic compounds, zinc, chromates, polyacrylates, polyacrylamides, polycarboxylates such as e.g. polymaleic anhydride, and adducts thereof.

For the purpose of preventing corrosion and stone deposits

in aqueous systems, a polyampholyte polymer with an intrinsic viscosity of 0.05-4.5 dl/g in 1.0 M NaCl is now provided, which is characterized by the fact that they are produced by polymerization of:

(i) 5 - 90% by weight of at least one carboxylic functional monomer of the formula:

where

R is hydrogen, phenyl, alkyl with 1-3 carbon atoms

or a group -COOX,

R^" is a branched or straight-chain carbon chain

with from 0 to 12 carbon atoms, and

X is hydrogen or an alkali metal or alkaline earth metal,

(ii) 0.5 - 85% by weight of at least one cationic monomer selected from the compounds with the general formulas:

where:

R is hydrogen, a phenyl group or an alkyl group with 1-3 carbon atoms, preferably hydrogen or methylene, 4 R is a straight chain or branched alkyl group with 1-12 carbon atoms, preferably 1-3 carbon atoms and X is an anion, preferably a halogen or alkyl sulfate, and (iii) 0-85% by weight of at least one non-ionic monomer of the formula:

where

R is hydrogen, phenyl or alkyl with 1-3 carbon atoms, and

R 2 , which may be the same or different, is hydrogen or alkyl of 1-3 carbon atoms.

The invention also relates to the use of the above-described polyampholyte polymer to inhibit corrosion and stone deposits in an aqueous system.

The polyampholyte polymers according to the invention have shown

are particularly useful for inhibiting deposits of calcium phosphate and polymerisation of silicon dioxide, but they also inhibit the formation of deposits of magnesium hydroxide, calcium chloride, calcium carbonate, calcium sulphate etc.

Examples of carboxylic functional monomers of

the carboxylic monomer(s) (i) which are applicable in the production of the polyampholyte polymers according to the invention are acrylic acid, crotonic acid, methacrylic acid, vinylacetic acid, allylacetic acid, 4-methyl-4-pentenoic acid and dicarboxylic acids such as maleic acid and itaconic acid and the alkali metal and alkaline earth salts thereof . The preferred carboxylic functional monomers are acrylic acid and methacrylic acid and the corresponding salts thereof. Also mixes of ds; carboxylic functional monomers can be used in the production of the polyampholyte polymers.

Examples of X in the above formulas for the cationic monomers (ii) are halogen, sulfate, sulfonate, phosphate, hydroxide, borate, cyanide, carbonate, thiocyanate, thiosulfate, isocyanate, sulfite, bisulfite, nitrate, nitrite, oxalate, silicon -cation, sulphide, cyanate, acetate and other common inorganic and organic ions.

Specific examples of the most preferred cation-containing monomers (ii) are diethyldiallylammonium chloride, dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium methylsulfate and methacrylamidopropyltrimethylammonium chloride. Mixtures of cationic monomers (ii) can also be used in the production of the polyampholyte polymers.

Examples of the non-ionic monomers (iii) are acrylamide and its derivatives, such as methacrylamide and N,N-dimethyl-acrylamide. The preferred nonionic monomer is acrylamide. Mixtures of non-ionic monomers (iii) can also be used in the production of the polyampholyte polymers.

The polyampholyte polymers can be prepared by mixing the monomers in the presence of a free radical initiator. Any free radical initiator can be used. Examples of such are peroxides, azo initiators and redox systems.

The preferred catalysts are sodium persulfate or a mixture of ammonium persulfate and any azo-type initiator such as 2,2'-azobis-(2,4-dimethyl)-4-methoxyvaleronitrile). The polymerization can also be initiated photochemically.

The polyampholyte polymers can be produced by a number of different methods, e.g. by solution polymerisation, suspension polymerisation, mass polymerisation and emulsion polymerisation.

The temperature is not of decisive importance. Reaction will usually take place at temperatures between 10 and 100°C, and the polymerization is preferably carried out at temperatures between 40 and 60°C. It is not usually practical to carry out the polymerization at a temperature below room temperature, as the polymerization in those cases is too slow. At temperatures above 60°C, the molecular weight of the polymer has a tendency to decrease. The reaction will, depending on the temperature, usually take from 1 to 12 hours. Measurements of the residual amounts of monomers will give an indication of when the reaction is complete.

The pH value of the reaction mixture is not of critical importance. The pH is usually in the range of 4.5 to 9.0.

It is difficult to accurately measure the molecular weight of polyampholyte polymers. The polymers are instead usually identified by their intrinsic viscosity. The intrinsic viscosity of the polyampholyte polymer according to the invention must be 0.05-4.5 dl/g in 1.0 M NaCl (measured in a Cannon Ubbelohde capillary viscometer).

In the production of the polyampholyte polymers according to the invention, it is preferred to use 22.5-70% by weight of the carboxylic functional monomer(s) (i), 2.5-25% by weight of the cationic monomer(s) (ii) and 1.5-85 % by weight, most preferably 5-67.5% by weight, of the non-ionic monomer(s) (iii).

The concentration of the polyampholyte polymer according to the invention, which is used to inhibit corrosion and scale deposits in aqueous systems, is generally at least 0.1 ppm and is preferably 0.1-500 ppm, calculated on the basis of the weight of the aqueous system being treated. Preferably, the concentration level will be from 1.0 to 200 ppm.

The aqueous system in which the polyampholyte polymers

are applicable to prevent corrosion and scale deposits, can be any aqueous system, e.g. a cooling water, a boiler water, the water in a desalination plant or the water in a gas scrubber system. If the system is a desalination system, the polyampholyte polymer should have an intrinsic viscosity lower than 2.8 dl/g in 1.0 M sodium chloride.

Below, the use of the new polyampholyte polymers will be described in more detail in a number of examples. However, the production of the polymers used in these examples must first be described.

Preparation of the polymers used in the examples.

The polyampholyte polymers were prepared by mixing anionic monomer (i), cationic monomer (ii) and non-ionic monomer (iii) in the quantities indicated in Table I, using the solids concentrations, initial temperatures and pH indicated there -values. The monomer mixture was flushed with nitrogen for 1 hour. Deionized water was used as solvent. The initiator was added, and the components were allowed to react for approx. 3 hours. The polymers 31-37 listed in Table I were prepared by mixing anionic monomer (i), cationic monomer (ii) and non-ionic monomer (iii) in the proportions given in Table I, after which the solutions were neutralized to pH 7.0 with 50% sodium hydroxide. Chain transfer agent and catalyst were added in the amounts indicated in Table I. The solutions were placed under fluorescent light for 60 minutes. The gels formed were diluted to 600 mg/l active polymer.

Examples 1-31 (cooling water)

The inhibition of calcium phosphate deposition was tested using 250 ppm Ca<++> and 6.0 mg/l PO^ with 10 ppm inhibitor, of pH 8.5 and at 60°C for 24 hours. The percent inhibition, shown in Table II, was determined by measuring the PO 3 concentration in the solution before and after a 24 hour period.

The percentage inhibition of calcium phosphate was measured using 2.5 ppm and 5 ppm inhibitor, following the method set forth in Examples 1-23. The results are shown in Table III.

Examples 32 - 40 (desalination)

Steam was passed through a metal U-tube to maintain the temperature at 151°C. The U-tube was immersed in a cylindrical cell. Seawater, with a concentration factor of 1.6 times normal seawater (of pH 8.2) was passed through the cell at a rate of 600 ml/h. After 24 hours, the stone deposit on the U-tube was removed, weighed and analyzed. The efficiency is indicated as the percentage inhibition, defined by the equation: % inhibition =

The provisions were determined by the equation:

The percentage inhibition achieved with a number of deposition inhibitor compositions is given in Table IV.

Examples 41 - 56 (cooling water)

Polymer 11 was added in amounts as indicated in Example V to samples of synthetic boiler water containing varying amounts of PO 4 OH , SiO 2 , Mg ++ and chelant (sodium nitrite-rilotriacetic acid). In each example, testing was carried out under three conditions: without any terpolymer, with 1 mg/ml terpolymer and with 10 mg/l terpolymer. The mixtures were heated to 90°C and kept at this temperature during the experiments. The pH value was kept between 10 and 12. Each sample was observed after 1 hour, 4 or 5 hours, and 21 or 22 hours. The observations are set out in table V. The experiment is used to predict the effectiveness of the inhibitors in boiler water systems. In the columns indicating the observations, A indicates the most preferred outcome, while F indicates the least preferred outcome.

Footnote to Table V

A ready

B small particles dispersed throughout the mixture

C small particles deposited on the bottom

D particles agglomerated on the bottom to the size of small

cotton balls

E particles agglomerated on the bottom to the size of a

medium sized cotton ball

F particles agglomerated on the bottom to the size of a large cotton ball

Examples 57 - 72 (gas scrubbers)

The zeta potential is a measure of the particle surface charge at the particle/water interface. An effective inhibitor will increase the charge and thus increase the repulsive force between particles. This will increase the dispersibility of the particles and reduce the coagulation, the sweeping and the subsequent deposition.

The zeta potentials of particles of magnetite (iron oxide) and of calcium carbonate and magnetite in a 70/30 weight mixture were determined for 1000 ppm suspensions in deionized water at varying pH values. 0.5 ppm and 5 ppm of different polymers were added to the suspensions and the Zeta potential was again measured. The change in Zeta potential after inhibitor addition, or the increase in Zeta potential, is indicated in Table VI. As the Zeta potential increased, more stable suspensions were formed. Mixed deposits of magnetite and calcium carbonate are particularly typical of deposits found in many gas scrubbing cisterns.

Examples 73 - 75 (silicon dioxide inhibition)

20.0 ml of 1.0 M sodium chloride, 8 ml of 0.1 M sodium silicate solution and optionally a predetermined amount of inhibitor were mixed and diluted with distilled water to a final volume of 100 ml. The temperature of the mixture was kept at approx. 40°C during the experiment, and the pH value was adjusted to 8.0 by adding hydrochloric acid. The silicon dioxide monomer concentration was determined by the molybdate method [Alexander, G.B.; J.A.C.S. 75, 5055

(1953)] after 5.0 minutes and later at certain intervals. The data were analyzed using a second order kinetic curve and the rate of polymerization was determined. Table VII shows the effect of the inhibitor on the silicon dioxide polymerization process. A reduction in this polymerization rate indicates an expected reduction in the amount of silicon dioxide deposition on heat transfer and water transport surfaces in aqueous systems.

Example 76 (- corrosion)

In the specimen immersion test, it was used

a cylindrical battery vessel with a capacity of 8 litres. A Haake immersion circulator (Model D-52)) for maintaining constant temperature was used to regulate the solution temperature and agitate the regulated bath. The unit contained a 1000 watt fully adjustable stainless steel heating device that allowed temperature control of -0.01°C,

and a pump with a capacity of 10 liters per minute and with built-in pressure nozzles to ensure a very even temperature in the bathroom. A contact thermoregulator was used as a temperature-sensing element.

The pH of the solution was regulated with a "Krugere and Eckels Model 440 pH Controller". This unit was capable of

to turn the power to a Dias mini pump on and off when the pH of the corrosive liquid medium dropped below the set point. The Dias peristaltic pump, with a pump capacity of 20 ml per hour, maintained the pH of the solution by adding sulfuric acid. Standard glass and saturated calomel electrodes were used as the recording elements. The bath was ventilated continuously at a rate of 60 cm 3 per minute through a medium porous plastic gas distribution tube to ensure air saturation.

Two SAE 1010 steel coupons, each with a surface area of 27.1 cm <2>, were suspended with a glass hook. The ratio between the volume of the solution and the surface area of the test metal in the experiment was approx. 1000:1.

The composition of the synthetic water used in the experiment was as follows, with the content indicated per liter of distilled water:

Ion: Ca<++> Mg<++> HCO~ Cl" SO^-

<ppm>: 88 24 40 70 328

The total hardness measured as CaCO 3 was 318 ppm, and the pH value was 7.5. The temperature was 50 C.

The test was conducted on a 2-3 day cycle basis and the system was treated with the corrosion inhibitor materials listed in Table I. After every two or three days the test solution was scrapped and a fresh solution was prepared. At the end of a 14 day cycle, the coupons were removed and analyzed and the experiment terminated. The degree of corrosion of the coupons was measured as their weight loss during a 14 day cycle, and the result was converted to mm per year. The test results are given in Table VIII.

Claims (3)

1. Polyampholyte polymers with intrinsic viscosity of 0.05-4.5 dl/gi 1.0 M NaCl, characterized in that they are produced by polymerization of: (i) 5 - 90% by weight of at least one carboxylic functional monomer with the formula: where R is hydrogen, phenyl, alkyl with 1-3 carbon atoms or a group -COOX,. R<1> is a branched or straight-chain carbon chain with from 0 to 12 carbon atoms, and X is hydrogen or an alkali metal or alkaline earth metal, (ii) 0.5 - 85% by weight of at least one cationic monomer selected from among the compounds with the general formulas: where: R 3 is hydrogen, a phenyl group or an alkyl group with 1-3 carbon atoms, preferably hydrogen or methylene, R 4 is a straight-chain or branched alkyl group with 1-12 carbon atoms, preferably 1-3 carbon atoms and X is an anion, preferably a halogen or alkyl sulfate, and (iii) 0-85% by weight of at least one non-ionic monomer with the formula: where R is hydrogen, phenyl or alkyl with 1-3 carbon atoms, and R 2 , which may be the same or different, is hydrogen or alkyl of 1-3 carbon atoms. 2. Use of a polyampholyte polymer according to claim 1 or a salt thereof to inhibit corrosion and stone deposits in an aqueous system. 3. Use according to claim 2 of a polyampholyte polymer prepared from 22.5-70% by weight of the carboxylic functional monomer(s) (i), 2.5-25% by weight of the cationic monomer(s) (ii) and 5-67% by weight % of the non-ionic monomer(s) (iii).